Filter elements for liquid filtration of viscous media such as oil or fuel are produced in a conventional way from pleated filter media preferably in a cylindrical shape. These filter elements can be free of metal and can be provided with an end plate of film, cardboard, plastic material, for example, PA, or something similar. Embodiments with metal end plates and a central metal tube are possible also. In this connection, the pleats of the filter elements are often incorporated into the end plates, for example, glued, welded, or foamed, and directly connect these elements.
The embodiments comprising a central tube for receiving the filter elements are often designed such that a reciprocal sealing action of the unfiltered side and the filtered side in the flow of the medium to be filtered is realized by means of an O-ring that is pushed onto the central tube; the O-ring is then exchangeable during servicing.
It is disclosed, for example, in DE 100 46 494 A1 to employ a metal-free filter element in an oil filter for filtering oil of an internal combustion engine. This filter element is inserted into a housing and the housing is closed off by a lid. In the housing, for reducing oil return upon shut-down of the internal combustion engine, a non-return vale is usually provided. In this connection, at least one seal is arranged on the filter element such that it rests seal-tightly against a housing wall of the filter housing within a predetermined axial movement area.
For preventing the filter housing from draining completely in the tube direction, it is also customary to employ a spring-loaded valve that is permanently introduced into the housing. These non-return valves are inserted in a separate assembly step into the housing and the non-return valves are comprised usually of a valve plate that is pre-tensioned by a spring; a valve crown; and a valve seat. The valve is screwed into the housing or inserted, wherein, generally, it is disadvantageous that assembly of this module is complex.
For example, DE 42 40 656 C2 disclose a further filtering arrangement for fuel and/or lubricants of an internal combustion engine in which a bottom drainage is provided that is closed off by an end plate of the filter element upon insertion of the filter element. This drainage is opened as soon as the filter element is removed so that the oil can flow out through this drainage bore into a catch basin. Also known in the prior art is a non-return valve that is comprised of a metal plate that is loaded by a spring and that seals the supply bore for the unfiltered oil. In this connection, different valve components are required.
Moreover, U.S. Pat. No. 5,413,712 discloses a filter for liquids in which the end plates of the cylindrical filter element are made from plastic material that is connected to the filter element. As a non-return diaphragm, an additional radially sealing rubber diaphragm is provided that rests against the end plate and is inserted during assembly.